A known fuel delivery system (British Patent 2,248,087 A) of has an air intake conduit with a throttle valve arranged in it, opening into an intake manifold from which intake tubes branch off to the individual combustion chambers of the internal combustion engine. Near the intake areas of the individual combustion chambers to inject fuel into the intake tubes to form a fuel-air mixture. An engine control unit controls the fuel injection as a function of the intake air volume through the air intake conduit, as well as other engine operating parameters.
Furthermore, the engine control unit acts on a central injection valve, with a respective fuel vaporizer installed upstream from the throttle valve on the air intake conduit, to supply vaporized fuel to the intake air.
During idling and partial-load operation of the internal combustion engine, the fuel-air mixture is formed by means of the central injection valve, whereas only the individual injection valves are used to supply fuel in high-load operation.
The problem with this approach is that a large portion of the fuel vapor generated during the warm-up phase after starting an internal combustion engine condenses upon intake into colder zones of the internal combustion engine and forms an unwanted wall film which leads to increased hydrocarbon emissions.
With another known fuel delivery system (German Patent Application No. 4,119,206 A1), an injection valve is provided near the intake area of each combustion chamber of an internal combustion engine to inject fuel into the respective intake tube or the intake area of the combustion chamber to form a fuel-air mixture. In addition, an air intake channel having a control valve is connected at the intake end of the air intake tube located upstream from a throttle valve. The air intake channel opens at the outlet end into the fuel outlet area of the respective injection valve.
In the warm-up phase of the internal combustion engine, air can be blown through the air intake channel into the fuel discharge area of the injection valve to support the atomization of fuel. The air supply through the air intake channel is regulated by the control valve as a function of the engine rpm, the intake vacuum, the engine temperature and/or other engine operating parameters.
With such a fuel delivery system, it is hardly possible to effectively prevent formation of a wall film of condensed fuel, which plays a significant role in hydrocarbon emissions during the warm-up phase after starting an internal combustion engine, i.e., when the engine is cold.
It is especially problematical that a greater amount of fuel must be supplied when the engine is cold than when it is hot to achieve an ignitable fuel-air mixture (with a certain proportion of vaporized fuel in the combustion chamber) because a large portion of the injected fuel condenses as a film on the various wall and thus does not contribute to the combustion, but instead is emitted as excess hydrocarbon in the exhaust. This causes an unwanted increase in hydrocarbon emissions during the warm-up phase of the internal combustion engine.